Studies on the thermal isomerization of N-arylmethylbenzotriazoles

Abstract

The thermal isomerizations of N-benzyl-, N-diarylmethyl- and N-trityl-benzotriazole, and of N-[bis-(4-methoxyphenyl)methyl]- and N-trityl-5,6-dimethylbenzotriazole under nitrogen have been investigated. In all these cases, the N-1 isomer predominates over the N-2 isomer at thermodynamic equilibrium, to an extent which depends on the steric bulk of the N-substituent. The rate of attainment of equilibrium depends on the electronic effects of the substituents, both in the benzotriazole ring and in the migrating group. These results, in conjunction with a cross-over experiment, support a mechanism involving a heterolytic N–C bond cleavage followed by an intermolecular rearrangement.